Process for the preparation of n-vinyl-carboxylic acid amides



United States Patent Int. Cl. C0711 27/06, 29/42, 41/06, 103/48 US. Cl.260-239.? 3 Claims ABSTRACT OF THE DISCLOSURE Preparation of N-vinylcarboxylic acid amides by reaction of acetaldehyde with carboxylic acidamides and splitting the N-(a-hydroxyethyl)-compounds so obtained byheating them in the presence of acidic catalysts forming N-vinyl amides.The novel process is distinguished by the fact thatthe N-vinyl amidesare obtained in a fast proceeding reaction and in high space-timeyields.

It is known that pyrrolidone reacts with acetaldehyde in the presence ofacid catalysts at elevated temperature to formethylidene-bis-pyrrolidone (Monatshefte f. Chemie, 87, Seite 367(1956)). It is known, too, that vinyl amides can be obtained by thesplitting of N-(u-alkoxyethyD-amides. However, the starting substancesmust first be prepared in the pure state (French Pat. No. 1,421,336).

It has now been found, that vinyl carboxylic acid amides of the generalformula wherein R represents a hydrogen atom, an alkyl group, preferablywith 1 to 4 carbon atoms, a cyclo alkyl-, aryl or aralkyl group, and Rrepresents an alkyl group containing 1 to 4 carbon atoms, and R and Rmay be linked as to form a ring of S to 8 ring members, can be obtainedby reacting first amides of the general formula R2 Rl-CN wherein R and Rhave the meanings given above, with acetaldehyde to formN-(a-hydroxyethyl)-compounds and by splitting said compoundssubsequently by heating in the presence of acid catalysts into thecorresponding vinyl amides.

Suitable starting substances are, for instance, N-methylformamide,N-ethylformamide, N-methylacetamide, N- methyl propionamide,pyrrolidone-2, piperidone-2, and e-caprolactam.

The first stage of the process consists in reacting the amide withacetaldehyde, preferably in the presence of catalysts, to formN-(a-hydroxyethyD-amide. The refractive index increases thereby. Thereaction temperature should not be over 90 C. Advantageously it rangesfrom 20-90 C., preferably from 30-70 C. If necessary, the reaction heatis dissipated by cooling. The reaction is terminated when the refractiveindex of the mixture does not change any more or only slightly.

The molar ratio between the amide and the acetaldhyde can be as desired;generally, it lies between 1:5 and 2:1. Molar ratios of 1:2 and 1:1 areof advantage. Preferably, the components are used in equimolecularquantities.

The first stage of the process is carried out at normal or elevatedpressure. Suitable catalysts are basic and acidic substances. As basiccatalysts there may be mentioned tertiary organic bases, for exampletriethylamine. Strongly basic ion exchangers in the base form may beused advantageously. Preference is given to strong bases such aspotassium or sodium hydroxide. Before carrying out the second stage ofthe process, the basic catalysts should suitably be removed orneutralized.

As acidic catalysts there may be used mineral acids, such ashydrochloric acid, sulfuric acid, phosphoric acid or polyphosphoricacids, and the acidic derivatives thereof, as sulfamic acid, carboxylicacids and sulfonic acids and the acidic derivatives thereof, such asoxalic acid, succinic acid, tartaric acid, citric acid, phthalic acidmonoethyl ester, hexadecyl sulfonic acid, toluene sulfonic acids,benzene-1,3-disulfonic acid and their semi-esters. Furthermore, theremay be used acidic or acidic hydrolyzing salts, such as sodium hydrogensulfate, alums, zinc chloride, cobalt chloride or aluminium chloride.Advantageously, there may be used strongly acidic cation exchangers inthe acid form. However, mineral acids or sulfonic acids are preferred asacidic catalysts. The quantity of the catalyst varies between 0.01 to10% by weight based on the amide employed. Generally, the quantitiesused are in the lower part of the said range when the catalysts aresoluble in the reaction mixture, and lie in the upper part when thecatalysts used are insoluble.

The second stage of the process is suitably carried out by heating theN-(a-hydroxyethyD-amide prepared in the first stage for a short time toa temperature higher than that applied during the first phase andranging from to 350 0., preferably from to 250 C. The pureN-(u-hydroxyethyD-amide can be used for the second stage. It is ofadvantage to use the reaction mixture obtained, according to the processof the invention, during the first stage. This reaction mixture will bereferred to in the following as M The reaction can be carried out bybringing into contact in a suitable way pure N-(a-hydroxyethyD-amide orM with the catalyst heated to the reaction temperature. This can be donefor example by introducing the N-(uhydroxyethyl)-amide or M into areaction vessel containing the catalyst preferably in a finely dispersedform or on appropriate supports such as broken tiles or diatomaceousearth. It is also possible to mix the N-(a-hydroxyethyD-amide or M withthe catalyst and to heat to the required temperature. M can be useddirectly with advantage if it still contains catalyst from the firststage of the reaction which can be used for the second.

It is of advantage, if the heating is brought about rapid ly, forexample by introducing the substances to be reacted in small quantities,for instance dropwise, by injections or spraying or mixed to a hotstream of gas, into a reaction vessel heated to the reactiontemperature. It is likewise of advantage to remove the reaction productsfrom the reaction zone according to their formation and to cool themquickly, if desired, so that there will be no or only minorside-reactions. Suitable devices for the second stage of the reactionare, for instance, rotary or thin-layer evaporators as well ascirculation tubes or heat exchangers having a low volume compared withthe flowing quantity.

The time for which the reaction mixture is exposed to the splittingtemperature varies generally from 0.1 second to 5 minutes,advantageously from 0.1 to 60 seconds and preferably from 0.1 to 10seconds. The reaction products are obtained by distillation. Ifnecessary, the raw product must be neutralized beforehand in casecatalyst has been carried along or a volatile acid been used.

Non-reacted starting substances can be recovered and used withoutfurther purification in the first stage of the reaction. As catalyststhere may be used all acidic catalysts which can be applied in the firststage. Non-volatile or diflicultly volatile mineral or sulfonic acidsare preferred.

The catalyst is used in quantities of 0.01 to by Weight, based on thereaction mixture. As for the quantity of catalyst to be used in aparticular case, the same indications must be observed as in the firststage. The second stage can be carried out at normal or reducedpressure, even at a slightly elevated pressure.

It was surprising that the reaction led to the desired vinylamides,since it had to be expected that, under the conditions of the secondreaction stage, the N-(a-hydroxyethyl)amides would decompose underreversal of the equation of formation into the starting substances.Likewise, it had to be expected, that thereby, especially because of thepresence of acid catalysts, exclusively ethylidene-bis-amides would haveformed as usual.

The process of the present invention is above all characterized by thefact that the desired N vinyl compounds are obtained in a fastproceeding reaction and in high space-time-yields. It can be carried outequally well discontinuously or continuously.

The N-vinyl amides obtained according to the process of the presentinvention are known compounds capable of being polymerized, according toknown methods, in substance or in solvents in the presence of radical orionic catalysts to products soluble or non-soluble in Water and inseveral organic solvents. The homoand co-polymerisates have foundvarious applications. They are used, for instance, as textileauxiliaries, adhesives, auxiliaries for dyeings, and solvents forpolyvinylchloride. Poly-N- vinyl lactams, especially can be used asbinding agents for light-sensitive components in photographic emulsions.The polymers of N-vinyl lactams and open chain vinylamides, used ascomponents in polyacrylo-nitrile fibers, improve their dyeability.Poly-N-vinylpyrrolidone is used in blood expanders.

The following examples illustrate the invention, but they are notintended to limit it thereto; the parts indicated are by Weight, unlessotherwise stated.

EXAMPLE 1 A mixture of 59 parts of N-methylformamide and 44 parts ofacetaldehyde (n =l.394) was heated with 1 part of polyphosphoric acid ascatalyst for 2 hours under reflux. The reaction mixture (n =1.443) washeated to 40 C. and then introduced dropwise into a thin-layerevaporator, the temperature of the latter being kept at 160 C. Thepressure was 4 to 6 mm. Hg. At a reactor capacity of 150 ml. thethroughput was 80-100 ml./hour. 95 parts of raw product were condensatedin the receivers. According to gas chromatographic analysis it contained33 parts of N vinyl N methylformamide and 30 parts of N-methylformamide.The conversion was 49%, the yield 80%, referred to the reacted amide.The raw product was neutralized and the vinylmethylformamide obtainedby, fractional distillation. Boiling point 45 C. at 14 mm. Hg.

N-methylacetamide can be obtained by the same method. The boiling pointof N-vinylmethylacetamide is 64 C. at 20 mm. Hg.

EXAMPLE 2 In a stirring vessel provided with a reflux condenser, 0.6part of pulverized potassium hydroxide was added to a mixture of 59parts of N-methylforrnamide and 44 parts of acetaldehyde, whilestirring. The temperature of the mixture rose soon and was kept under 70C. by cooling. The reaction was terminated in about 45 minutes. 1 partof phosphoric acid of 90% strength was dissolved in the reaction mixture(n =1.445), the latter being reacted, as described in Example 1, in athin-layer evaporator at 160 C. 93 parts of raw product were obtainedcontaining 4 27 parts of N vinyl N methylformamide and 35 parts ofN-methylformamide. 41% of the formamide had been reacted. The yield ofvinyl amide was 79% EXAMPLE 3 In a flask provided with a refluxcondenser, a mixture of parts of pyrrolidone and 44 parts ofacetaldehyde (n =1.430) was added to 1.3 parts of polyphosphoric acid,while stirring. The temperature of the mixture increased and was keptbelow 50 C. by cooling. After 45 minutes, the reaction mixture (n=l.482) was reacted, as described in the preceding examples, in athin-layer evaporator. The reaction temperature was 200 C., the pressure2-4 mm. Hg. At a reactor capacity of ml. the throughput was 150-170rnl./hour. The raw product, 116 parts, contained 24 parts of pyrrolidoneand 56 parts of N-vinylpyrrolidone. 72% of the amide were reacted. Theyield of the vinyl compound was 70%. Purification of thevinylpyrrolidone was effected by fractional distillation. Boiling point87 C. at 10 mm. Hg.

EXAMPLE 4 In a stirring vessel provided with a reflux condenser, 0.3part of pulverized potassium hydroxide Was added to a mixture of 85parts of pyrrolidone and 44 parts of acetaldehyde, While stirring. Thetemperature of the mixture increased at an initially strong reflux andwas kept below 70 C. by cooling. After about 30 minutes, the reactionwas terminated. 1.4 parts of polyphosphoric acid were dissolved in thereaction mixture obtained (n =1.487) and the latter introduced into athin-layer evaporator. The reaction temperature was 200 C., the pressure3-5 mm. Hg. 114 parts of distillate were obtained containing, accordingto gas chromatographic analysis, 24 parts of pyrrolidone and 54 parts ofN-vinylpyrrolidone, which, at a conversion of 72%, corresponded to ayield of 68%, referred to the pyrrolidone reacted. Before beingsubjected to fractional distillation, the distillate had beenneutralized with a sodium methylate solution.

EXAMPLE 5 83 parts of N-(oz-hydroxyethyl)-pyrrolidone were separatedfrom the cooled reaction mixture, obtained according to Example 4, as acrystalline substance (melting point 4446 C.). 0.9 part ofpolyphosphoric acid was dissolved therein by heating and the mixture wasreacted in a thin-layer evaporator at 200 C. and 2-4 mm. Hg. Thethroughput was 150-170 ml. at a reactor capacity of 150 ml. 74 parts ofdistillate were obtained containing, according to gas chromatographicanalysis, 17 parts of pyrrolidone and 34 parts of N-vinyl pyrrolidone.This corresponded to a yield of 70%, referred to non-recoveredpyrrolidone. 1

EXAMPLE 6 A mixture of 113 parts of e-caprolactam, 44 parts ofacetaldehyde and 1.5 parts of polyphosphoric acid were stirred for 1hour in a flask provided with reflux condenser. By that time thecaprolactam had dissolved. The temperature increased and was kept, bycooling, below 60 C. An oily homogeneous reaction mixture, having arefractive index of n =1.484 had formed. This mixture was preheated to40-50 C. and then reacted in a thin-layer evaporator heated to 220 C. ata pressure of 2-4 mm. Hg. 146 parts of the raw product were condensatedin the receivers. The partly crystalline product was taken up inmethanol and, what catalyst had been carried along, soon neutralized.According to gas chromatographic analysis it contained 35 parts ofN-vinyl caprolactam and 74 parts of caprolactam, which corresponded to ayield of 70%, calulated on the reacted lactam. The reaction rate was 350.

EXAMPLE 7 A mixture of 59 parts of N-methylformamide and 44 parts ofacetaldehyde was heated in the presence of 1 part of polyphosphoric acidas catalyst for 4 hours to 35-40 C. The reaction mixture (n -=1.444) wasintroduced within minutes at normal pressure into a thin-layerevaporator kept at a temperature of 210 C. According to gaschromatographic analysis, the distillate contained parts ofN-methylformamide and parts of N-vinyl-N- methylformamide, whichcorresponded to a conversion of 49% and a yield of 84%.

EXAMPLE 8 590 parts of N-methylformamide, 440 parts of acetaldehyde and52 parts of polyphosphoric acid were stirred for 4 hours in a vesselwith reflux condenser. The temperature of the mixture increased slowlyand was kept, by cooling, below C. The reaction mixture was introducedinto a thin-layer evaporator, the temperature of which being maintainedat 120125 C. The pressure was 6-8 mm. Hg. The throughput was 10-12liter/hour, at a capacity of the evaporator of 5 liters. The raw productwas obtained by fractional distillation. 398 parts ofN-vinyl-N-methylformamide were isolated. 266 parts of methylformamidewere recovered. The conversion was 55%, the yield 84%.

We claim:

1. Process for preparing a N-vinylcarboxylic acid amide of the formulawherein R represents hydrogen or alkyl containing 1 to 4 carbon atoms, Rrepresents alkyl containing 1 to 4 carbon atoms and R and R when joinedrepresent alkylene forming a ring with 5 to 8 ring members, whichcomprises reacting between 20 and C. and at a molar ratio of between 1:5and 2:1 an amide and acetaldehyde wherein the amide is of the formulawherein R and R have the meanings defined above, formingN-(u-hydroxyethyl)-amides and thereafter forming said N-vinyl carboxylicacid amides from said N-(a-hydroxyethyl)-amides by heating the last at atemperature between C. and 350 C. for 0.1 second to 60 seconds in thepresence of only an acidic catalyst to produce the vinyl amides.

2. The process as claimed in claim 1, wherein the amide and acetaldehydeare reacted in the presence of a triethylamine, strongly basic ionexchangers in the base form, sodium hydroxide, potassium hydroxide,mineral acids, a carboxylic acid, a sulfonic acid, hexadecyl sulfonicacids, toluene sulfonic acids, a benzene disulfonic acid and itssemi-ester, or strongly acidic cation exchangers in the acid form.

3. The process as claimed in claim 1, wherein the N-(a-hydroxyethyD-amide is heated in the presence of hydrochloric acid,sulfuric acid, phosphoric acid, polyphosphoric acids, sulfamic acid, amono carboxylic acid, oxalic acid, succinic acid, tartaric acid, citricacid, phthalic acid monoethyl ester, hexadecyl sulfonic acid, toluenesulfonic acids, benzene-1,3-disulfonic acid and the semi-esters of saiddifunctional acids, sodium hydrogen sulfate, alums, zinc chloride,cobalt chloride, aluminum chloride or strongly acidic cation exchangersin the acid form.

Smith: The Chemistry of Open Chain Organic Nitrogen Compounds, vol. 1(Benjamin) (1965).

HENRY -R. JILES, Primary Examiner R. T. BOND, Assistant Examiner US. Cl.X.R.

